Thermal processing is common in the semiconductor industry. Thermal treatments are used to activate chemical and physical changes in semiconductor substrates to reorganize the atomic structure and composition of the substrate. In a commonly used approach known as Rapid Thermal Processing, the substrate is heated to a target temperature at a rate up to 400° C./sec, held at the target temperature for a short time such as 1 sec, and then rapidly cooled to a temperature below which no further changes occur.
To promote uniform processing of all areas of the substrate, temperature sensors are commonly deployed to monitor temperature at various locations of the substrate. Pyrometers are widely used to measure the temperature of the substrate. Control and measurement of substrate temperature, and therefore of local layer formation conditions, is complicated by thermal absorptions and light emissions by chamber components and exposure of sensors and chamber surfaces to processing conditions inside the processing chamber. There remains a need for a thermal processing chamber with improved temperature control, temperature measurement, and methods of operating such a chamber to improve uniformity and repeatability.